Abstract

Alkaline earth oxonitride perovskites EAMO(2)N (EA = Sr, Ba;M = Nb, Ta) were synthesized by the ammonothermal method at temperatures of 900 K and maximum pressures of up to 300 MPa in custom-built autoclaves starting from Nb or Ta and Sr or Ba metals. The reactions were performed under ammonobasic conditions using NaN3 and NaOH as mineralizers. Powder X-ray diffraction and Rietveld refinement were used to determine the crystal structures. The elemental composition and morphology of the obtained products were investigated by scanning electron microscopy and energy-dispersive X-ray spectroscopy. Crystals of 1-10 mu m size were obtained. Optical band gap values were determined from UV/Vis measurements applying the Kubelka-Munk function with the Tauc method (E-g = 1.9 - 2.1 eV). In addition to that, ANb/Ta(O,N)(3) with A = Ca, Sr, Ba, La were synthesized by ammonolysis reactions of the respective ternary oxide precursors. The products were investigated with N-14 solid-state (MAS) NMR spectroscopy, all showing a single resonance at about 270 ppm.